Re: smaller speakers
Most speaker manufacturers make good, better, best quality speakers...so yes you can get good quality 5.25" speakers. I think your real question is will they sound the same as an equivalent pair of 6.5" speakers? No they won't simply because of the reduce speaker cone surface area. This leads to okay mid and highs but bass tones suffer. You will definitely be able to hear them fine but you will not have much bass. The 6.5" speakers will only be a little better. For truly noticeable bass you need sub-woofers.